1. Technical Field
The present invention relates to a printer and an ink sheet, and more particularly to a printer that produces an image for transfer purpose (hereinafter called a “transfer image”) on an intermediate transfer sheet by use of an ink sheet on which a plurality of single colors of ink are repeatedly arranged in a longitudinal direction of the sheet and that produces a desired image by means of transferring the transfer image of the intermediate transfer sheet onto a subject to be printed (hereinafter simply called a “subject”) as well as to an ink sheet used for the printer.
2. Related Art
A hitherto-known printer produces a transfer image on an intermediate transfer sheet by use of an ink sheet on which a plurality of single colors of ink are repeatedly arranged in a longitudinal direction of the sheet and transfers to a subject the transfer image on the intermediate transfer sheet, thereby producing a desired image.
As shown in FIG. 8, JP 2005-131954 A discloses use of an ink sheet 20 on which four colors of ink; namely, black (BK) ink, cyan (C) ink, magenta (M) ink, and yellow (Y) ink are repeatedly arranged in such a way that different colors adjoin each other in a longitudinal direction of the sheet. Further, when an image is produced in a single color by means of transferring to an image formation area of the intermediate transfer sheet single color ink BK that is the first color of the ink sheet 20, a thermal printer head transfers the same single color BK of ink from the ink sheet 20 to the intermediate transfer sheet, thereby creating a position mark. The position mark is used for registration between an intermediate transfer sheet and a thermal printer head and registration between the intermediate transfer sheet and a subject. The position mark is formed at a side of each image formation area; namely, a position that is located between a rear of a leading end and a forward of a trailing end of each image formation area and, and outside the image formation area.
In order to perform registration of respective colors of ink while a boundary between the colors of ink is made definite, boundary marks must be provided among the single colors of ink. For instance, as shown in FIG. 9, a conceivable method is to place marks 82 among the single colors of ink and a different mark 80 at a boundary of a single color BK of ink that is the first color. The mark 80 is formed by means of notching a portion of the single color BK of ink; in other words, causing a portion of the single color BK of ink to protrude in a longitudinal direction. The mark 82 is formed from two black lines spaced apart from each other by a predetermined distance. As a result of the marks 80 and 82 being formed as mentioned above, two sensors for detecting the position of the ink sheet 20 detect reflectance along a line “a” and a line “b” in the drawing, so that the start of each single color of ink can be detected in accordance with a difference between the reflectance detected from the area “a” and the reflectance detected from the area “b.” In short, in relation to the single color BK of ink, a portion of the line “a” is notched, and the line “a” exhibits high reflectance at that portion, and the line “b” exhibits low reflectance. The start of the single color BK of ink can be detected by detection of this pattern. In the meantime, in relation to the next mark 82, a black line is present along the line “a,” and no black line is present along the line “b.” Hence, the line “a” exhibits low reflectance, and the line “b” exhibits high reflectance. Thus, an inverse pattern appears. Accordingly, the start of the next single color C of ink can be detected by detection of the pattern. Light passes through an area where ink (a black line) is not present, and light reflected from a reflection plate is detected. In reality, a sensor of light emission type is utilized. Light does not pass through an area where there is a black ink provided along a boundary between single colors of ink, and reflected light cannot be received. In contrast, light passes through an area where there is not a black line (and a notched area), and light reflected from a reflection plate can be received, whereupon the start of each color of ink is detected.
However, when the marks 80 and 82 are formed on the ink sheet 20 as mentioned above, areas where ink is present become asymmetrical with respect to the longitudinal center axis of the sheet, and the thickness of black ink becomes accumulated. Unevenness arises in the diameter of an ink ribbon, and the sheet becomes eventually prone to wrinkling. An imperfect image (a decolored image attributable to wrinkles) may arise in the intermediate transfer sheet. Specifically, an ink ribbon requires about 2500 turns. If unevenness exists in the thickness of a sheet in a widthwise direction thereof, a difference of a take-up diameter (a diameter) that is 5000 times as large as an ordinary diameter will arise. On the assumption that the thickness of ink is 0.6 μm, unevenness of about 3 mm arises in a take-up diameter because of presence or absence of ink. If such an ink ribbon is pulled as it is, the diameter will change according to a position with respect to the widthwise direction, so that wrinkles may arise in the sheet.
In the related art, when an image is produced in a single color by means of transferring the single color BK of ink; namely, the first color of the ink sheet 20, to an image formation area of the intermediate transfer sheet, the thermal printer head transfers the same single color BK of ink from the ink sheet 20 to the intermediate transfer sheet, thereby creating a position mark. However, there arises a problem of the entire length of the ink sheet 20 becoming longer by an amount corresponding to the single color BK of ink. Namely, black can also originally be expressed by means of three colors of ink; that is, C, M, and Y. However, if the singe color BK of ink is deleted, there will arise a problem of the inability to produce a position mark.